Sir Michael Scholar, chairman of the UK Statistics Authority, took the unusual step of publishing a highly critical letter to George Osborne over concerns that loose procedures in the Treasury may damage confidence in the national statistics.

He also urged the Chancellor to pare back the number of people who receive the figures a day early to prevent them being used for political “spin”.

The agency, Britain’s statistics watchdog, ordered the Treasury to investigate its processes after sensitive inflation data this month was sent to 400 unauthorised people 17 hours before its release.

Sir Michael warned: “There is a risk of market manipulation if key economic data fall in to the wrong hands before publication.”

Speculation that the Office for National Statistics (ONS) data was leaking to the market has been rising. Market rumours correctly predicted the last two consumer price inflation releases – in April and May – even though economists’ forecasts were wildly out.

The ONS “found no evidence of a leak, but there can never be positive proof that the suspicions were unfounded, so the damage to public confidence in these most important economic statistics remained”, Sir Michael said. There was no Treasury “laspse” with the April data.

However, its error this month was the second time this year that it had disseminated ONS numbers early. In February, producer price Indices were sent to the same 400 people a day early. After the first mistake, the Treasury tightened up its procedures.

However, the second failure was a human error. “So far as can be ascertained, no-one made personal or political profit from it,” Sir Michael said.

Sir Michael used the leaks issue to launch a wide-ranging attack on the Chancellor for politicising the data.

“None of these suspicions, leaks or suspected leaks could have occurred if the Government had stuck to the position it took in Opposition: namely that you should reduce pre-release access to the minimum, so that only those who really need to know are shown these statistics in advance of general publication,” he said.

“A return to your earlier position would do much to restore trust in official statistics, and would, I believe, be helpful to trust in government as a whole.”

About 50 people see the data early, including 15 Treasury officials and two in Number 10.

Sir Michael added: “There is, I believe, no good reason, but successive governments want the political advantage that such prior knowledge confers on them: that is, time to work out their line; and therefore time to spin.”

When in Opposition, the Conservatives had taken the line that pre-release should be limited to avoid political abuse of the figures.

Mark Hoban, now Financial Secretary to the Treasury, said in 2007: “I can tell you from personal experience that pre-release is constantly used by the government to divert the media away from numbers which make for uncomfortable reading. It allows pre-emptive spin, with government departments sometimes putting out data designed to contradict evidence about to be revealed by the industrious, independent boffins from the ONS.”

However, the Treasury is not believed to be considering changes to the pre-release arrangements.

Referring to the unauthorised data release, a spokesman said: “This was an accidental breach by the official side of the Treasury, no ministers were involved and no-one made personal or political profit from this mistake. The Treasury has put in place stringent measure to make it less likely this mistake will happen in the future.”